The interaction between transmission and distribution networks is increasingly important, so it is necessary to consider the coordination between them in planning. In this paper, a coordinated planning method of a transmission and distribution network based on an Alternating Direction Method of Multipliers (ADMM) and optimal power flow (OPF) is proposed. In this method, the OPF of the network is taken into account, the transmission power at the connection of the transmission and distribution network is taken as the coupling variable to establish the coordination planning model, and the coupling variable is taken as the shared variable. Then, a sub-algorithm is proposed to independently divide the power supply network of each substation in the preliminary scheme of the distribution network side planning and obtain the final scheme, so as to optimize the preliminary scheme. Finally, the final planning scheme of the two sides is integrated. Through the simulation analysis of the coupling system between the IEEE-14 bus system and the 54-node distribution network, and the comparison of the network planning scheme without considering the coordination of transmission and distribution network, the rationality and effectiveness of the method in this paper are verified. This work is supported by National High-tech R & D Program of China (863 Program) (No. 2015AA050101).